The invention relates to a blade segment of a disc refiner intended for refining lignocellulose material used in the production of fibrous material such as paper and board, with the blade segment comprising an inner circumference and an outer circumference as well as a first side edge and a second side edge which combine the inner circumference and the outer circumference.
A disc refiner consists of two or more opposite refining elements, at least one of which refining elements is rotatable. The rotating refining element can be referred to as a rotor, and the non-rotating, or stationary, refining element can be referred to as a stator. Between the refining elements is a refining gap, where the material to be refined is ground against the refining surfaces. The refining surface of the refining elements comprises blade bars and blade grooves. The refining surface is constituted by attaching one or more blade elements to the frame structure of the refining element, with the blade element having a refining surface which comprises blade bars and blade grooves. In stationary refining elements, said blade element can also be attached directly to the frame structure of the refiner. The refining surface of the refining element can consist of one uniform blade element, in which case a single individual annular planar blade element can constitute an entire refining surface of a refining element. Conventionally, the refining surface of the refining element of a disc refiner is, however, constituted of several planar blade segments placed side by side, in which case each blade segment on its own constitutes only some portion of the complete annular refining surface of the refining element, and the blade segments placed side by side together constitute the complete annular refining surface of the refining element.
A typical blade segment comprises an inner circumference of the blade segment directed in the direction of the inner circumference of the refining element and an outer circumference of the blade segment directed in the direction of the outer circumference of the refining element, and a first side edge of the blade segment and a second side edge of the blade segment connecting the inner circumference and the outer circumference of the blade segment, where the first side edge and the second side edge are straight, i.e. in the radial direction of the blade segment so that the blade segment resembles the shape of a sector of a ring. It is typical for said blade segments that the side edges of the blade segments constitute a point of discontinuity at the interface or at the point of contact of adjacent blade segments, which can result for example in disturbances both in the actual refining and in the flow of the material that is to be refined and that has been refined at the interfaces of adjacent blade segments and in their vicinity. Moreover, in order to ensure the structural strength of the blade bars, there is a need to make reinforcements when moving from one blade segment to another. There are also prior art blade segments where the side edges are not straight, i.e. not in the radial direction of the blade segment, but instead in the vicinity of the inner circumference the side edge is in the radial direction and then turns at one point away from the radial direction against the intended direction of rotation of the blade segment. Such a construction requires precise tolerances at the interfaces of the blade segments so that unrefined pulp would not escape through the refiner.